An inherent hazard with conventional filing cabinets having a number of horizontally slidable drawers is that if more than one drawer is pulled out at a given time, the cabinets may tip. Accordingly, a number of systems have been developed which prevent the opening of further drawers once a first drawer has been opened.
Some of the earlier systems, for example, those described in U.S. Pat. Nos. 4,480,883 (Young) and 4,298,236 (Laroche) utilize locking cams which are rotatable by the action of an actuator arm from a closed position, wherein they have a first effective height, to an open position wherein they have a second greater effective height. These systems further use vertically slidable locking rods extending between adjacent locking cams and include stop means which limit movement of the locking rods so that only one of the cams may be rotated into the open position at any given time.
In the system disclosed in Young, the locking cams are freely floating between adjacent locking rods and have opposed flanges which engage the locking rods to prevent the locking cams from falling out. A disadvantage with this system is that if any of the locking rods should be separated, for example, if they stick, the locking cams may then come out. A further disadvantage to this system is that dimensional inaccuracies of the components are additive so that actuator arm placement becomes more inaccurate the further up the cabinet one goes. Furthermore, the system disclosed in Young requires that separate upper and lower limits be provided for the locking rods.
In the structure disclosed in the Laroche reference, the locking cams are mounted on fixed pivot axis which are provided by pivot pins extending between the locking rod supporting channel and a bracket attaching to the interior surface of the cabinet and extending across the locking rod supporting channel. As the locking cams in Laroche are not freely floating, Laroche provides a recess in the upper ends of the locking rods which will receive the lower portion of the cam immediately thereabove when the stack of rods is raised. A disadvantage with the Laroche system is that opposite ends of the pin on which the cam pivots attach to different members. Accordingly, if the pin locating holes in either of the members are not accurately placed, the pins will not properly align. Furthermore, it is necessary in assembling the device disclosed in the Laroche reference to provide a pin and furthermore to install each pin individually during the manufacture of the cabinet.